I'm pretty sure it was designed for champion who easily proc Spellblade effects on champions, hence the fact that it's a Spellblade-esque effect that only procs on champions.
Which would mean it's designed mostly for ranged champions, but melee champions that can trade easily or have a faux-ranged attack like Gangplank also get to benefit from it.
Y'know, just like how Electrocute is designed mostly for ranged champions that can toss an ability or two in between autoattacks, but also works for melee champions that have enough attack speed or a multi-part burst combo to also proc it easily.
Or just like how Press the Attack is designed mostly for ranged champions for them to get extra damage while kiting or chasing someone down, but also works for melee champions that have enough sticking power to keep wailing on someone while they try to run away.
Like ... ranged champions are basically the default to design around due to the lack of disadvantages they have. Melee champions sometimes get extra benefits ( it's really not the way around ) so that they can have tools that full power without also giving access to those tools to ranged champion at full power, but that's ... not really necessary on everything, especially on something already pretty niche.